1. Field of the Invention
The present invention relates to a device which includes a ceramic thin plate member, containing a fired ceramic sheet, and a metal thin plate member supporting the ceramic thin plate member and which is used in, for example, solid oxide fuel cells.
2. Background of the Invention
Conventionally, a thin plate member containing a fired ceramic sheet (hereinafter also referred to as a “ceramic thin plate member”) has been used in various apparatuses (devices) such as sensors, actuators, and solid oxide fuel cells (SOFCs). For example, when a ceramic thin plate member is applied to an SOFC, the ceramic thin plate member is composed of a solid electrolyte layer of zirconia, which is a ceramic; a fuel electrode layer formed on one face of the solid electrolyte layer; and an air electrode layer formed on the other face of the solid electrolyte layer. Further, a fuel passage or channel is formed to face the fuel electrode layer, and an air passage or channel is formed to face the air electrode layer. Such a ceramic thin plate member for SOFC is joined to a holding frame formed of a thin metal plate (hereinafter also referred to as a “metal thin plate member”) at the periphery thereof, and is held by the metal thin plate member. An outer circumferential portion of the metal thin plate member is supported by a support member.
The metal thin plate member has a curved portion formed through press working or the like. The curved portion is formed to surround the perimeter of the ceramic thin plate member. In other words, the curved portion is formed on the metal thin plate member such that the crest of the curved portion extends continuously so as to form a ridge portion, and the ridge portion surrounds the ceramic thin plate member (the circumference thereof) (see, for example, Japanese Patent No. 3466960, FIG. 6).
Incidentally, in some cases, for example, when an SOFC is caused to quickly start power generation, the temperature of a device (a ceramic thin plate member and a metal thin plate member) changes sharply. As a result, a difference in thermal expansion is produced between the ceramic thin plate member and the metal thin plate member. A thermal stress generated due to the difference in thermal expansion mainly acts on a joint portion between the ceramic thin plate member and the metal thin plate member and/or on the ceramic thin plate member. Although the above-described conventional metal thin plate member has the curved portion, the metal thin plate member cannot deform to sufficiently relax the thermal stress acting on the joint portion and/or on the ceramic thin plate member, because the crest (ridge portion) of the curved portion is formed to surround the ceramic thin plate member. Therefore, in some cases, the joint portion between the ceramic thin plate member and the metal thin plate member and/or the ceramic thin plate member may be broken.
Further, in the conventional metal thin plate member, since the curved portion is formed to surround the ceramic thin plate member, the curved portion hardly functions to improve the rigidity of the metal thin plate member in a direction perpendicular to the plane of the ceramic thin plate member. Therefore, when the curved portion thermally expands and relaxes the above-mentioned thermal stress, the curved portion deforms not only in a direction within the plane of the ceramic thin plate member but also in a direction perpendicular to the plane of the ceramic thin plate member. As a result, the thermally expanded curved portion is likely to move the ceramic thin plate member in the direction perpendicular to the plane of the ceramic thin plate member. Accordingly, even in a case where the joint portion and/or the ceramic thin plate member is not broken, there may arise a problem that the ceramic thin plate member moves or deforms in a direction perpendicular to its plane, and closes a corresponding fuel passage or air passage. Moreover, even in a case where the ceramic thin plate member moves or deforms to a degree such that the fuel passage or air passage is not completely closed, there may arise a problem that the moved or deformed ceramic thin plate member increases the pressure loss of fuel, the loss being produced when the fuel flows through the fuel passage, and/or the pressure loss of fluid, such as air, the pressure loss being produced when the fluid flows through the air passage.
If the joint portion is broken or the ceramic thin plate member deforms as described above, the apparatus has lower the performance or lower reliability.